U.S. patent application number 11/220587 was filed with the patent office on 2007-01-04 for cipher method and system for multicast service.
This patent application is currently assigned to Industrial Technology Research Institute. Invention is credited to Yu-Ching Hsu, Chia-Chin Lin, Shiao-Li Tsao.
Application Number | 20070005958 11/220587 |
Document ID | / |
Family ID | 37591218 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070005958 |
Kind Code |
A1 |
Hsu; Yu-Ching ; et
al. |
January 4, 2007 |
Cipher method and system for multicast service
Abstract
A cipher method and system for multicast service. A group
includes multiple user equipment, each having a respective key. The
keys are orthogonal to one another. A content provider provides a
raw message to the user equipment of the group. A BM-SC server has
a key set composed of the respective keys of all user equipment of
the group to encipher the raw message to thus obtain an enciphered
message for broadcast. All user equipment of the group receives and
deciphers the enciphered message with the respective keys. When a
user equipment leaves the group, the key set held by BM-SC is
updated by removing the key of the leaving user equipment.
Inventors: |
Hsu; Yu-Ching; (Shueilin
Township, TW) ; Lin; Chia-Chin; (Chaojhou Township,
TW) ; Tsao; Shiao-Li; (Taipei City, TW) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
US
|
Assignee: |
Industrial Technology Research
Institute
Hsinchu
TW
|
Family ID: |
37591218 |
Appl. No.: |
11/220587 |
Filed: |
September 8, 2005 |
Current U.S.
Class: |
713/163 |
Current CPC
Class: |
H04L 63/065 20130101;
H04L 63/0428 20130101; H04L 2209/601 20130101; H04L 9/0833
20130101 |
Class at
Publication: |
713/163 |
International
Class: |
H04L 9/00 20060101
H04L009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2005 |
TW |
094122281 |
Claims
1. A cipher system for multicast service, comprising: a group,
which has multiple user equipments with respective keys orthogonal
to one another; a content provider, which provides a message to the
user equipments of the group; and a broadcast multi-service center
(BM-SC) server, which has a key set composed of the keys of all
user equipments of the group to accordingly encipher the message
provided by the content provider so as to obtain an enciphered
message for broadcast, such that all user equipments of the group
receive and decipher the enciphered message with the respective
keys, thereby correctly receiving the message.
2. The system as claimed in claim 1, wherein the BM-SC server
enciphers the message provided by the content provider with an
enciphering function f(d, K)=d*(SUM(K)), where d represents
original data of the message, SUM is an addition function, and *
indicates a multiplication.
3. The system as claimed in claim 2, wherein all user equipments of
the group deciphers the enciphered message with a deciphering
function g(c, k.sub.i)=c*k.sub.i/||k.sub.i||, where k.sub.i
indicates the respective key of a user equipment, c represents
enciphered data of the message, and ||k.sub.i|| indicates a length
of the key k.sub.i.
4. The system as claimed in claim 1, wherein the BM-SC server
removes the respective key of a user equipment from the key set
when the user equipment leaves the group.
5. A cipher method for multicast service, the multicast service
using a content provider to provide a message to multiple user
equipments of a group, a broadcast multi-service center (BM-SC)
server to encipher the message provided by the content provider to
thus obtain an enciphered message for broadcast, and the user
equipments of the group to receive and decipher the enciphered
message, the method comprising the steps of: (A) assigning a
respective key to each user equipment of the group, wherein the
respective keys are orthogonal to one another; (B) providing a
message by the content provider; (C) using the broadcast
multi-service center (BM-SC) server to encipher the message with a
key set composed of the respective keys of all user equipments of
the group, thereby obtaining an enciphered message for broadcast;
and (D) receiving and deciphering the enciphered message with the
respective keys of the user equipments of the group, thereby
correctly receiving the message.
6. The method as claimed in claim 5, wherein the BM-SC server in
step (C) enciphers the message provided by the content provider
with an enciphering function f(d, K)=d*(SUM(K)), where d represents
original data of the message, SUM is an addition function, and *
indicates a multiplication.
7. The method as claimed in claim 6, wherein all user equipments of
the group in step (D) deciphers the enciphered message with a
deciphering function g (c, k.sub.i)=c*k.sub.i/||k.sub.i||, where
k.sub.i indicates the respective key of a user equipment, c
represents enciphered data of the message, and ||k.sub.i||
indicates a length of the key k.sub.i.
8. The method as claimed in claim 5, further comprising: (E) using
the BM-SC server to remove the respective key of a user equipment
from the key set when the user equipment leaves the group.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a technical field of multicast
service and, more particularly, to a cipher method and system for
multicast service.
[0003] 2. Description of Related Art
[0004] The 3rd Generation Partnership Project (3GPP) has
recommended the Multimedia Broadcast Multicast Service (MBMS), as
shown in the configuration of a typical MBMS (multicast service)
system of FIG. 1. In order to send a message to N user equipments
UE.sub.1-UE.sub.n of a special group 12, the message provided by
the content provider 11 is enciphered and broadcasted by a
broadcast multi-service center (BM-SC) server 14. All user
equipments in the system can receive the enciphered message but
only the N user equipments UE.sub.1-UE.sub.n of the special group
12 can have a key k.sub.A to decipher the enciphered message and
accordingly receive the message. Thus, the content provider 11 can
send the message to the N user equipments UE.sub.1-UE.sub.n of the
special group 12, and the MBMS is achieved.
[0005] In the cited MBMS, each user equipment
UE.sub.1.about.UE.sub.n of the group 12 has the same key k.sub.A to
decipher the enciphered message. However, when a user equipment
UE.sub.1 leaves the group 12, the member of the group 12 is
changed. In this case, the key k.sub.A has to be changed to make
sure that only the user equipments UE.sub.2.about.UE.sub.n included
in the updated group 12 can have a new key k.sub.B. However, such
an updated procedure needs to use the BM-SC server 14 to update the
key in a unicast manner for each user equipment
UE.sub.2.about.UE.sub.n, which results in a lot of signaling
overhead and time delay. Especially, when the users of the group
increase, the probability of member change in the group is
relatively increased, which further causes the system to change the
key frequently.
[0006] Therefore, it is desirable to provide an improved cipher
method and system for multicast service to mitigate and/or obviate
the aforementioned problems.
SUMMARY OF THE INVENTION
[0007] The object of the invention is to provide a cipher method
and system for multicast service, which can make it as an
independent event when a user of a group leaves the group and thus
does not cause the problem of changing a new key for each remaining
user of the group.
[0008] In accordance with one aspect of the invention, a cipher
system for multicast service is provided. The system includes a
group, which has multiple user equipments with respective keys
orthogonal to one another; a content provider, which provides a
message to the user equipments of the group; and a broadcast
multi-service center (BM-SC) server, which has a key set composed
of the keys of all user equipments of the group to accordingly
encipher the message provided by the content provider so as to
obtain an enciphered message for broadcast, such that all user
equipments of the group receive and decipher the enciphered message
with the respective keys, thereby correctly receiving the
message.
[0009] In accordance with another aspect of the invention, a cipher
method for multicast service is provided. The multicast service
uses a content provider to provide a message to multiple user
equipments of a group, a broadcast multi-service center (BM-SC)
server to encipher the message provided by the content provider to
thus obtain an enciphered message for broadcast, and the user
equipments of the group to receive and decipher the enciphered
message. The method includes the steps of (A) assigning a
respective key to each user equipment of the group, wherein the
respective keys are orthogonal to one another; (B) providing a
message by the content provider; (C) using the broadcast
multi-service center (BM-SC) server to encipher the message with a
key set composed of the respective keys of all user equipments of
the group, thereby obtaining an enciphered message for broadcast;
and (D) receiving and deciphering the enciphered message with the
respective keys of the user equipments of the group, thereby
correctly receiving the message.
[0010] Other objects, advantages, and novel features of the
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a block diagram of a configuration of a typical
multicast service system; and
[0012] FIG. 2 is a block diagram of a configuration of a multicast
service system in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] With reference to FIG. 2, there is shown a block diagram of
a configuration of a multicast service system according to the
invention. As shown in FIG. 2, a content provider 11 provides a
message to user equipments UE.sub.i (i=1.about.n) of a special
group 12, wherein each user equipment UE.sub.i possesses a
respective key k.sub.i (i=1.about.n), and the keys are orthogonal
to one another. The message provided by the content provider 11 is
enciphered by a broadcast multi-service center (BM-SC) server 14
for broadcast, and received by the user equipments UE.sub.i of a
specific group 12 for deciphering with the respective key k.sub.i.
Thus, the message sent by the content provider 11 is correctly
received by the user equipments UE.sub.i of the specific group 12,
and so as to achieve the multicast service in which messages from
the content provider 11 can be sent to the user equipments UE.sub.i
of the specific group 12.
[0014] In the system, each user equipment UE.sub.i of the specific
group 12 is assigned with a different key k.sub.i, and the keys are
orthogonal to one another (having orthogonal feature, i.e., a
product of two keys is zero). The BM-SC server 14 has a key set
K={k.sub.1, k.sub.2, k.sub.3, . . . k.sub.n} composed of the keys
of all user equipments UE.sub.i of the group 12. The message
provided by the content provider 11 is enciphered by the BM-SC
server 14 with an enciphering function f(d, K)=d*(SUM(K)) for
broadcast, where d represents original data of the message, SUM is
an addition function, and * indicates a multiplication.
[0015] When an enciphered message is received by each user
equipment UE.sub.i of the group 12, a deciphering function g(c,
ki)=c*k.sub.i/||k.sub.i|| is applied for deciphering the enciphered
message, where c is the enciphered data obtained from enciphering
the message, and ||k.sub.i|| indicates a length of key k.sub.i.
[0016] The enciphering function f(d, K)=d*(SUM(K)) performs an
enciphering by summing all keys k.sub.i of the user equipments
UE.sub.i of the group 12 and then multiplying the summation with d.
Conversely, on deciphering, since the keys k.sub.i assigned to the
user equipments UE.sub.i are orthogonal to one another, a product
of the keys is obtained as k.sub.i*k.sub.j=0 for either two of the
user equipments UE.sub.i and UE.sub.j of the group 12, where
k.sub.i, k.sub.j belong to K, and k.sub.i*k.sub.i=||k.sub.i||.
Thus, the deciphering function g(c, k.sub.i)=c*k.sub.i/||k.sub.i||
can accurately restore the original data of the message. Further,
when a user equipment UE.sub.x that does not belong to the group 12
tries to decipher the enciphered message with a key k.sub.x, it
cannot work because the key k.sub.x does not belong to the key set
K.
[0017] With the aforementioned encipher method, when a user
equipment UE.sub.1 leaves the group 12, only the key k.sub.1 of the
user equipment UE.sub.1 is removed from the key set K included in
the BM-SC server 14 (K={k.sub.2, k.sub.3, k.sub.4, . . . k.sub.n}),
without changing a new key for each existing user. In this case,
even the user equipment UE.sub.1 uses the key k.sub.1 to decipher,
it cannot work because the key k.sub.1 does not belong to the key
set K any more.
[0018] An example is given for further description of the
invention, wherein a group 12 includes user equipments UE.sub.1,
UE.sub.2 and UE.sub.3 with the respective keys k.sub.1=(3,0,0),
k.sub.2=(0,2,0) and k.sub.3=(0,0,5), and thus the key set
K={k.sub.1, k.sub.2, k.sub.3} is obtained, where the key kI has a
length of nine, the key k2 has a length of four, and the key k3 has
a length of 25. The content provider 11 provides a message with
original data d=8, which is enciphered by the BM-SC server 14 with
the enciphering function as follows. f .function. ( d , K ) = d * (
SUM .function. ( K ) ) = 8 * ( SUM .function. ( k 1 , k 2 , k 3 ) )
= 8 * ( ( 3 , 0 , 0 ) + ( 0 , 2 , 0 ) + ( 0 , 0 , 5 ) ) = 8 * ( 3 ,
2 , 5 ) = ( 24 , 16 , 40 ) = c . ##EQU1##
[0019] The enciphered data c is broadcasted by the BM-SC server 14.
The user equipments UE.sub.1, UE.sub.2 and UE.sub.3 can decipher c
with the respective keys k.sub.1=(3,0,0), k.sub.2=(0,2,0) and
k.sub.3=(0,0,5), thereby obtaining the original data d as follows:
UE.sub.1: (24,16,40)*(3,0,0)/9=72/9=8 UE.sub.2:
(24,16,40)*(0,2,0)/4=32/4=8 UE.sub.3:
(24,16,40)*(0,0,5)/25=200/25=8.
[0020] In this case, when a user equipment UE.sub.4 tries to
decipher c with a key k.sub.4=(2,0,0) that does not belong to the
key set K={k.sub.1, k.sub.2, k.sub.3}, it results in
(24,16,40)*(2,0,0)/4=48/4=12.noteq.8.
[0021] In addition, when the user equipment UE.sub.1 leaves the
group 12, the BM-SC server 14 removes the key k.sub.1 of the user
equipment UE.sub.1 from the key set K, and thus a new key set
K={k.sub.2, k.sub.3} is obtained. At this point, the content
provider 11 provides another message with original data d=7, which
is further enciphered by the BM-SC server 14 with the enciphering
function as follows: f .function. ( d , K ) = d * ( SUM .function.
( K ) ) = 7 * ( SUM .function. ( k 2 , k 3 ) ) = 7 * ( ( 0 , 2 , 0
) + ( 0 , 0 , 5 ) ) = 7 * ( 0 , 2 , 5 ) = ( 0 , 14 , 35 ) = c .
##EQU2##
[0022] The enciphered message c is broadcasted by the BM-SC server
14. The user equipments UE.sub.2 and UE.sub.3 can decipher c with
the respective keys k.sub.2=(0,2,0) and k.sub.3=(0,0,5), thereby
obtaining the original data d as follows: UE.sub.2:
(0,14,35)*(0,2,0)/4=28/4=7 UE.sub.3:
(0,14,35)*(0,0,5)/25=175/25=7.
[0023] However, the user equipment UE.sub.1 left deciphers c with
the key k.sub.1=(3,0,0) not belong to the new key set K to thus
obtain d=(0,14,35)*(3,0,0)/9=0/9=0.noteq.7.
[0024] From the above description, it is known that the invention
assigns the keys orthogonal to one another to each user of a
specific group, enciphers original data with an enciphering
function f(d, K)=d*(SUM(K)), and deciphers the original data with
an deciphering function g(c, ki)=c*k.sub.i/||k.sub.i||.
Accordingly, it is regarded as an independent event when a user
leaves the group, which does not cause the problem of changing a
new key for each remaining user of the group.
[0025] Although the present invention has been explained in
relation to its preferred embodiment, it is to be understood that
many other possible modifications and variations can be made
without departing from the spirit and scope of the invention as
hereinafter claimed.
* * * * *